Upstream frame configuration for ethernet passive optical network protocol over coax (EPoC) networks

ABSTRACT

A method and system for generating a data frame in an upstream frame in an Ethernet Passive Optical Network protocol over Coax (EPoC) network is provided. The data frame includes a plurality of resource blocks, each of a particular type. The resource blocks are arranged in the data frame in accordance with pilot rules and a pilot pattern.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/642,263, filed Mar. 9, 2015, which claims the benefit of U.S. Provisional Patent Application No. 61/950,054, filed Mar. 8, 2014, U.S. Provisional Patent Application No. 61/981,549, filed Apr. 18, 2014, and U.S. Provisional Patent Application No. 62/001,569, filed May 21, 2014, all of which are incorporated herein by reference in their entireties.

This application also claims the benefit of U.S. Provisional Patent Application No. 62/001,572, filed May 21, 2014, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This application relates generally to Ethernet, including Ethernet Passive Optical Network Over Coax (EPoC).

BACKGROUND

A Passive Optical Network (PON) includes a shared optical fiber and inexpensive optical splitters to divide the fiber into separate strands feeding individual subscribers. An Ethernet PON (EPON) is a PON based on the Ethernet standard. EPONs provide simple, easy-to-manage connectivity to Ethernet-based, IP equipment, both at customer premises and at the central office. As with other Gigabit Ethernet media, EPONs are well-suited to carry packetized traffic. An Ethernet Passive Optical Network Protocol Over Coax (EPoC) is a network that enables EPON connectivity over a coaxial network.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments.

FIG. 1 illustrates an example hybrid Ethernet Passive Optical Network (EPON)-Ethernet Passive Optical Network Over Coax (EPoC) network architecture.

FIG. 2 illustrates another example hybrid EPON-EPoC network architecture.

FIG. 3 illustrates an example EPoC portion of a hybrid EPON-EPoC network according to an embodiment of the present disclosure.

FIG. 4 illustrates an exemplary EPoC network.

FIG. 5 illustrates an example of a PHY auto-negotiation and link up procedure according to an embodiment of the present disclosure.

FIG. 6 illustrates an example upstream frame configuration according to an embodiment of the present disclosure.

FIG. 7 illustrates three different types of resource blocks that span 8 OFDMA symbols in time in accordance with embodiments of the present disclosure.

FIG. 8 illustrate three different types of resource blocks that span 16 OFDMA symbols in time in accordance with embodiments of the present disclosure.

FIG. 9 illustrates an example upstream data frame that adheres to specified pilot rules in accordance with embodiments of the present disclosure.

FIG. 10 illustrates an example upstream data frame that adheres to specified pilot rules in accordance with embodiments of the present disclosure.

FIG. 11 illustrates an example computer system that can be used to implement aspects of the present disclosure.

The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the disclosure.

References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

For purposes of this discussion, the elements in FIGS. 1-4 shall be understood to include software, firmware, or hardware (such as one or more circuits, microchips, processors, and/or devices), or any combination thereof. In addition, it will be understood that each element in FIGS. 1-4 can include one, or more than one, component within an actual device, and each component that forms a part of the described module can function either cooperatively or independently of any other component forming a part of the module. Conversely, multiple elements described herein can represent a single component within an actual device. Further, components within an element can be in a single device or distributed among multiple devices in a wired or wireless manner.

I. Example Hybrid EPON-EPoC Network Architectures

FIG. 1 illustrates an example hybrid Ethernet Passive Optical Network (EPON)-Ethernet Passive Optical Network Over Coax (EPoC) network architecture 100 according to an embodiment of the present disclosure. As shown in FIG. 1, example network architecture 100 includes an Optical Line Terminal (OLT) 102, an optional optical passive splitter 106, a communications node 110 including a coaxial media converter (CMC) 112, an optional amplifier 116, an optional coaxial splitter 118, a coaxial network unit (CNU) 122, and a plurality of subscriber media devices 124.

OLT 102 sits at a central office (CO) of the network and is coupled to a fiber optic line 104. OLT 102 may implement a DOCSIS (Data Over Cable Service Interface Specification) Mediation Layer (DML) which allows OLT 102 to provide DOCSIS provisioning and management of network components (e.g., CMC and Optical Network Unit (ONU)). Additionally, OLT 102 implements an EPON Media Access Control (MAC) layer (e.g., IEEE 802.3ah).

Optionally, optical passive splitter 106 can be used to split fiber optic line 104 into a plurality of fiber optic lines 108. This allows multiple subscribers in different geographical areas to be served by the same OLT 102 in a point-to-multipoint topology.

Communications node 110 serves as a converter between the EPON side and the EPoC side of the network. Accordingly, communications node 110 is coupled from the EPON side of the network to a fiber optic line 108 a, and from the EPoC side of the network to a coaxial cable 114. In an embodiment, communications node 110 includes a coaxial media converter (CMC) 112 that allows EPON to EPoC (and vice versa) conversion.

CMC 112 performs physical layer (PHY) conversion from EPON to EPoC, and vice versa. In an embodiment, CMC 112 includes a first interface (not shown in FIG. 1), coupled to fiber optic line 108, configured to receive a first optical signal from OLT 102 and generate a first bitstream having a first physical layer (PHY) encoding. In an embodiment, the first PHY encoding is EPON PHY encoding. CMC 112 also includes a PHY conversion module (not shown in FIG. 1), coupled to the first interface, configured to perform PHY layer conversion of the first bitstream to generate a second bitstream having a second PHY encoding. In an embodiment the second PHY encoding is EPoC PHY encoding. Furthermore, CMC 112 includes a second interface (not shown in FIG. 1), coupled to the PHY conversion module and to coaxial cable 114, configured to generate a first radio frequency (RF) signal from the second bitstream and to transmit the first RF signal over coaxial cable 114.

In EPoC to EPON conversion (i.e., in upstream communication), the second interface of CMC 112 is configured to receive a second RF signal from CNU 122 and generate a third bitstream therefrom having the second PHY encoding (e.g., EPoC PHY encoding). The PHY conversion module of CMC 112 is configured to perform PHY layer conversion of the third bitstream to generate a fourth bitstream having the first PHY encoding (e.g., EPON PHY encoding). Subsequently, the first interface of CMC 112 is configured to generate a second optical signal from the fourth bitstream and to transmit the second optical signal to OLT 102 over fiber optic line 108.

Optionally, an amplifier 116 and a second splitter 118 can be placed in the path between communications node 110 and CNU 122. Amplifier 116 amplifies the RF signal over coaxial cable 114 before splitting by second splitter 118. Second splitter 118 splits coaxial cable 114 into a plurality of coaxial cables 120, to allow service over coaxial cables of several subscribers which can be within the same or different geographic vicinities.

CNU 122 generally sits at the subscriber end of the network. In an embodiment, CNU 122 implements an EPON MAC layer, and thus terminates an end-to-end EPON MAC link with OLT 102. Accordingly, CMC 112 enables end-to-end provisioning, management, and Quality of Service (QoS) functions between OLT 102 and CNU 122. CNU 122 also provides multiple Ethernet interfaces that could range between 10 Mbps to 10 Gbps, to connect subscriber media devices 124 to the network. Additionally, CNU 122 enables gateway integration for various services, including VOIP (Voice-Over-IP), MoCA (Multimedia over Coax Alliance), HPNA (Home Phoneline Networking Alliance), Wi-Fi (Wi-Fi Alliance), etc. At the physical layer, CNU 122 may perform physical layer conversion from coaxial to another medium, while retaining the EPON MAC layer.

According to embodiments, EPON-EPoC conversion can occur anywhere in the path between OLT 102 and CNU 122 to provide various service configurations according to the services needed or infrastructure available to the network. For example, CMC 112, instead of being integrated within node 110, can be integrated within OLT 102, within amplifier 116, or in an Optical Network Unit (ONU) located between OLT 102 and CNU 122 (not shown in FIG. 1). When CMC 112 is implemented in OLT 102 at the CO hub, OLT 102 may be more aptly referred to as a Cable Line Terminal (CLT).

FIG. 2 illustrates another example hybrid EPON-EPoC network architecture 200 according to an embodiment of the present disclosure. In particular, example network architecture 200 enables simultaneous FTTH (Fiber to the Home) and multi-tenant building EPoC service configurations.

Example network architecture 200 includes similar components as described above with reference to example network architecture 100, including an OLT 102 located in a CO hub, a passive splitter 106, a CMC 112, and one or more CNUs 122. OLT 102, splitter 106, CMC 112, and CNU 122 operate in the same manner described above with reference to FIG. 1.

CMC 112 sits, for example, in the basement of a multi-tenant building 204. As such, the EPON side of the network extends as far as possible to the subscriber, with the EPoC side of the network only providing short coaxial connections between CMC 112 and CNU units 122 located in individual apartments of multi-tenant building 204.

Additionally, example network architecture 200 includes an Optical Network Unit (ONU) 206. ONU 206 is coupled to OLT 102 through an all-fiber link, comprised of fiber lines 104 and 108 c. ONU 206 enables FTTH service to a home 202, allowing fiber optic line 108 c to reach the boundary of the living space of home 202 (e.g., a box on the outside wall of home 202).

Accordingly, example network architecture 200 enables an operator to service both, ONUs and CNUs using the same OLT. This includes end-to-end provisioning, management, and QoS with a single interface for both fiber and coaxial subscribers. In addition, example network architecture 200 allows for the elimination of the conventional two-tiered management architecture, which uses media cells at the end user side to manage the subscribers and an OLT to manage the media cells.

II. Example Coaxial EPoC Link

FIG. 3 illustrates an example implementation 300 of an EPoC portion of a hybrid EPON-EPoC network. Example implementation 300 may be an embodiment of the EPoC portion of example EPON-EPoC network 100, described in FIG. 1, or example EPON-EPoC network 200, described above in FIG. 2. As shown in FIG. 3, the EPoC portion includes an EPoC CMC 112 and an EPoC CNU 122, connected via a coaxial network 304.

EPoC CMC 112 includes an optical transceiver 308, a serializer-deserializer (SERDES) 310, an EPoC PHY 312, including, in an embodiment, a CMC interface 314 and a modulator/demodulator 316, a controller 318, an analog-to-digital converter (ADC) 322, digital-to-analog converters (DAC) 320, and an radio frequency (RF) transceiver 326, including RF transmit (TX) circuitry 336 and RF receive (RX) circuitry 338.

Optical transceiver 308 may include a digital optical receiver configured to receive an optical signal over a fiber optic cable 302 coupled to CMC 112 and to produce an electrical data signal therefrom. Fiber optic cable 302 may be part of an EPON network that connects CMC 112 to an OLT, such as OLT 102. Optical transceiver 308 may also include a digital optical laser to produce an optical signal from an electrical data signal and to transmit the optical signal over fiber optic cable 302.

SERDES 310 performs parallel-to-serial and serial-to-parallel conversion of data between optical transceiver 308 and EPoC PHY 312. Electrical data received from optical transceiver 308 is converted front serial to parallel for further processing by EPoC PHY 312. Likewise, electrical data front EPoC PHY 312 is converted from parallel to serial for transmission by optical transceiver 308.

EPoC PHY 312, optionally with other modules of CMC 112, forms a two-way PHY conversion module. In the downstream direction (i.e., traffic to be transmitted to EPoC CNU 122), EPoC PHY 312 performs PHY level conversion from EPON PHY to coaxial PHY and spectrum shaping of downstream traffic. For example, CMC interface 314 may perform line encoding functions, Forward Error Correction (FEC) functions, and framing functions to convert EPON PHY frames into EPoC PHY frames for downstream transmissions to CNU 122. Modulator/demodulator 316 may modulate the data received from SERDES 310 using either a single carrier or multicarrier modulation technique (e.g., orthogonal frequency division multiplexing (OFDM), orthogonal frequency division multiple access (OFDMA), sub-band division multiplexing, etc.). When using a multicarrier technique modulator/demodulator 316 can perform multicarrier functions, including determining sub-carriers for downstream transmission, determining the width and frequencies of the sub-carriers, selecting the modulation order for downstream transmission, and dividing downstream traffic into multiple streams each for transmission onto a respective sub-carrier of the sub-carriers. In the upstream direction (i.e., traffic received from EPoC CNU 112), EPoC PHY 312 performs traffic assembly and PHY level conversion from coaxial PHY to EPON PHY. For example, modulator/demodulator 316 may assemble streams received over multiple sub-carriers to generate a single stream. Then, CMC interface 314 may perform line encoding functions, FEC functions, and framing functions to convert EPoC PHY frames into EPON PHY frames.

Controller 318 provides configuration, management, and control of EPoC PHY 312, including CMC interface 314 and modulator/demodulator 316. In addition, controller 318 registers CMC 112 with the OLT servicing CMC 112. In an embodiment, controller 318 is an ONU chip, which includes an EPON MAC.

DAC 320 and ADC 322 sit in the data path between EPoC PHY 312 and RF transceiver 326, and provide digital-to-analog and analog-to-digital data conversion, respectively, between EPoC PHY 312 and RF transceiver 326.

RF transceiver 326 allows CMC 112 to transmit/receive RF signals over coaxial network 304. In other embodiments, RF transceiver 326 may be external to CMC 112. RF TX circuitry 336 includes RF transmitter and associated circuitry (e.g., mixers, frequency synthesizer, voltage controlled oscillator (VCO), phase locked loop (PLL), power amplifier (PA), analog filters, matching networks, etc.). RF RX circuitry 338 includes RF receiver and associated circuitry (e.g., mixers, frequency synthesizer, VCO, PLL, low-noise amplifier (LNA), analog filters, etc.).

EPoC CNU 122 includes RF transceiver 326, including RF TX circuitry 336 and RF RX circuitry 338, DAC 320, ADC 322, an EPoC PHY 328, including modulator/demodulator 316 and a CNU interface 330, an EPoC MAC 332, and a PHY 334.

RF transceiver 326, DAC 320, ADC 322, and modulator/demodulator 316 may be as described above with respect to EPoC CMC 112. Accordingly, their operation in processing downstream traffic (i.e., traffic received from CMC 112) and upstream traffic (i.e., traffic to be transmitted to CMC 112), which should be apparent to a person of skill in the art based on the teachings herein, is omitted.

CNU interface 330 provides an interface between modulator/demodulator 316 and EPON MAC 332. As such, CNU Interface 330 may perform coaxial PHY level decoding functions, including line decoding and FEC decoding, and framing functions to generate EPoC PHY frames for upstream transmission. EPON MAC 332 implements an EPON MAC layer, including the ability to receive and process EPON Operation, Administration and Maintenance (OAM) messages, which may be sent by an OLT and forwarded by CMC 112 to CNU 122. In addition, EPON MAC 332 interfaces with a PHY 334, which may implement an Ethernet PHY layer. PHY 334 enables physical transmission over a user-network interface (UNI) 306 (e.g., Ethernet cable) to a connected user-equipment.

It should be noted that, in an alternate network configuration, CMC 112 can be implemented within an OLT at the CO hub, such as within OLT 102 shown in FIG. 1. In such an instance, it will be apparent to one of ordinary skill in the art that the implementation of CMC 312, shown in FIG. 3, can be modified to accommodate such a change. As noted above, when CMC 112 is implemented in an OLT, the OLT may be more aptly referred to as a Cable Line Terminal (CLT).

III. EPoC PHY Auto-Negotiation and Link Up

The EPON standard defines an ONU registration procedure for pure EPON networks. This, procedure is a MAC-level only procedure and thus is not sufficient to enable proper operation of an EPoC network because the physical layer is not addressed. Specifically, the coaxial portion of an EPoC network requires an auto-negotiation to determine the coaxial link spectrum, link bandwidth, and power level, and to establish precise timing between the CMC (or CLT) and the CNU. For example, in an EPON network, a link is designed to work at 1 Gbps or 10 Gbps. In an EPoC network, the coaxial link will likely be limited to a lower bandwidth, which needs to be discovered before the link can be used. In addition, this auto-negotiation, should be compatible with the EPON standard, which governs MAC-level interaction.

In the following, a PHY auto-negotiation and link up procedure for an exemplary EPoC network 400 illustrated in FIG. 4 is described. The PHY auto-negotiation and link up procedure is preferably compliant with the EPON standard and is performed between a CMC (or CLT) EPoC PHY 402 and CNU EPoC PHYs 404 over (at least) a shared coaxial medium 406. The PHY auto-negotiation and link up procedure can be further used to enable periodic maintenance of the links between the CMC (or CLT) EPoC PHY 402 and the CNU EPoC PHYs 404. CMC EPoC PHY 402 can be implemented in a CMC similar to CMC 112, and one or more of CNU EPoC PHYs 404 can be implemented in CNUs similar to CNU 122 described above with reference to FIG. 3.

Referring now to FIG. 5, an example of the PHY auto-negotiation and link up procedure 500 is illustrated. As shown in FIG. 5, the procedure 500 begins at step 502, which includes the CMC (or CLT) EPoC PHY 402 periodically broadcasting a link information (info) broadcast message over the coaxial medium 406 to the CNU EPoC PHYs 404. As mentioned above, data is generally transmitted over an EPoC network, using a multi-carrier or multi-channel transmission technique, such as orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA). The CMC (or CLT) EPoC PHY 402 is configured to broadcast the link info message over one or more carriers or channels, collectively referred to as the downstream PHY link channel, of the EPoC transmission spectrum. This downstream PHY link channel is dedicated to carrying PHY auto-negotiation and link information (and no MAC-level data) to limit interference with the MAC-level operation of the network.

The link info broadcast message can include several pieces of link information. For example, the link info broadcast message can provide link information regarding the modulation mode used and the duplexing mode used (e.g. time division duplexing or frequency division duplexing). If the modulation used is multicarrier modulation, the link information can further include the configuration of sub-carriers in the EPoC spectrum used to carry MAC-level data and control messages in the upstream and/or downstream direction. This configuration information can include all (or some) of the information required for the CNU PHY to be able to receive MAC-level data and control messages. For example, the configuration information can include the location in the EPoC spectrum of active downstream and upstream sub-carriers, the total number of sub-carriers, which sub-carriers carry data and/or pilots, and the sub-carriers respective modulation orders, as well as the location of any inactive sub-carriers in the EPoC spectrum. The link info broadcast message can further provide possible PHY configurations and capabilities, including an interleaver depth and a forward error correction type and size. In addition, when the downstream PHY link channel is used to convey timing information, it can carry time stamp information. In addition, the downstream PHY link channel can be used to carry power management messages. In this case, the downstream PHY link channel can carry information on wake-up times and modes, or moving into standby or sleeping mode, for each of the CNUs using unicast or broadcast messages. In addition, where OFDM is used to encode data transmitted in either the downstream or upstream direction, the configuration information can include, in addition, to the parameters already mentioned, the number of sub-carriers per OFDM symbol, the center frequency of the sub-carriers that make up OFDM symbols, and the size of any cyclic prefix added to OFDM symbols.

In step 506, unlinked ones of the CNU EPoC PHYs 404 are configured to “hunt” in the EPoC spectrum to locate the downstream PHY link channel and receive the link info broadcast message transmitted by the CMC (or CLT) EPoC PHY 402. The unlinked ones of the CNU EPoC PHYs 404 can “hunt” in the EPoC spectrum, for example, by looking for a predetermined preamble or bit pattern transmitted by the CMC (or CLT) EPoC PHY 402 at various frequencies to identify the downstream PHY link channel.

After unlinked ones of the CNU EPoC PHYs 404 locate the downstream PHY link channel and receive/decode the link info broadcast message from the CMC (or CLT) EPoC PHY 402, the unlinked ones of the CNU EPoC PHYs 404 can respond to the link info broadcast message using, for example, an echo protocol to perform auto negotiation and link up. An echo protocol can be used to provide a mechanism to share access to the coaxial medium 406 in the upstream direction between the unlinked ones of the CNU EPoC PHYs 404. For example, in the event that two or more unlinked ones of the CNU EPoC PHYs 404 attempt to respond to the link info broadcast message at the same time, the unlinked ones of the CNU EPoC PHYs 404 can implement random back off times to resolve the contention.

At step 506, an unlinked one of the CNU EPoC PHYs 404 will respond to the link info broadcast message by transmitting a reply message (e.g., an “echo” or copy of the link info broadcast message) upstream to the CMC (or CLT) EPoC PHY 402. The reply message can include a preamble to allow the CMC (or CLT) EPoC PHY 402 to determine initial range timing and transmit power of the unlinked one of the CNU EPoC PHYs 404 and an address of the unlinked one of the CNU EPoC PHYs 404. The address of the unlinked one of the CNU EPoC PHYs 404 can be the Ethernet MAC address of its associated CNU (or at least a portion of the Ethernet MAC address) or some other configurable address, for example. The reply message is sent during an upstream PHY discovery window, which is described further below in regard to the upstream frame configuration shown in FIG. 6.

At step 508, the CMC (or CLT) EPoC PHY 402 receives and processes the reply message from the unlinked one of the CNU EPoC PHYs 404 and, using the address provided in the received message, sends a link configuration unicast message back to the unlinked one of the CNU EPoC PHYs 404. The link configuration unicast message can include additional configuration settings to adjust, for example, the transmit power and a transmit delay of the unlinked one of the CNU EPoC PHYs 404.

More specifically, for the transmit delay, the CMC (or CLT) EPoC PHY 402 can monitor the time it takes from the last link info broadcast message it sends to the time it takes to receive the reply message from the unlinked one of the CNU EPoC PHYs 404 and, based on this time, determine an adjustment to the transmit delay in the unlinked one of the CNU EPoC PHYs 404. The adjustment can be determined to align upstream symbol transmissions from the unlinked one of the CNU EPoC PHYs 404 with the upstream, symbol transmissions of the other CNU EPoC PHYs 404 operating on the network. This adjustment value can be provided as a configuration setting in the link configuration unicast message sent by the CMC (or CLT) EPoC PHY 402 over the downstream PHY link channel at step 508.

Similarly, for the transmit power setting, the CMC (or CLT) EPoC PHY 402 can monitor the power level of the reply message received from the unlinked one of the CNU EPoC PHYs 404 and, based on this power level, determine an adjustment to the transmit power in the unlinked one of the CNU EPoC PHYs 404 to further optimize the data rate and/or hit-error rate of the shared upstream channel. Again, this adjustment value can be provided as a configuration setting in the link configuration unicast message sent by the CMC (or CLT) EPoC PHY 402 ever the downstream PHY link channel at step 508.

At step 510, the unlinked one of the CNU EPoC PHYs 404 receives and decodes the link configuration, unicast message and makes adjustments to, for example, its transmit power level and transmit delay based on the values in the decoded message. In addition, the unlinked one of the CNU EPoC PHYs 404 is configured to respond by transmitting a reply message (e.g., an “echo” or copy of the link configuration unicast message or another appropriate response) upstream to the CMC (or CLT) EPoC PHY 402. The reply message includes status information of the unlinked one of the CNU EPoC PHYs 404. This status information can include, for example, an error indicator or an indication of the power level of the messages the unlinked one of the CNU EPoC PHYs 404 is receiving from the CMC (or CLT) EPoC PHY 402. The reply message sent at step 510 can be sent over an upstream PHY link channel.

At step 512, the CMC (or CLT) EPoC PHY 402 receives and processes the reply message and status information sent by the unlinked one of the CNU EPoC PHYs 404 and responds by transmitting another link configuration unicast message over the DS PHY link channel. This link configuration unicast message can inform the unlinked one of the CNU EPoC PHYs 404 to transition to a linked state. For example, if the power level and symbol timing of the reply message to the link configuration unicast message the CMC (or CLT) EPoC PHY 402 receives at step 512 from the unlinked one of the CNU EPoC PHYs 404 are acceptable, the CNU EPoC PHYs 404 can send the link configuration unicast message over the DS PHY link channel to inform the unlinked one of the CNU EPoC PHYs 404 to transition to a linked state. Otherwise, if the power level and symbol timing are not acceptable, CMC (or CLT) EPoC PHY 402 can go back, to step 508 and send another link configuration unicast message to the unlinked one of the CNU EPoC PHYs 404 to adjust the transmit power and/or the transmit delay of the unlinked one of the CNU EPoC PHYs 404.

Assuming that the CMC (or CLT) EPoC PHY 402 sent a link configuration unicast message to the unlinked one of the CNU EPoC PHYs 404 to inform it to transition to a linked state at step 512, at step 514 the unlinked one of the CNU EPoC PHYs 404 can respond to this message by transmitting a reply message (e.g., an “echo” or copy of the link configuration unicast message it just received) upstream to the CMC (or CLT) EPoC PHY 402. The reply message includes status information indicating that the unlinked one of the CNU EPoC PHYs 404 is now linked and ready to transmit and receive EPON MAC-level messages. The reply message can be sent upstream over the upstream PHY link channel, which is described further below in regard to the upstream frame configuration shown in FIG. 6.

It should be noted that after (or even before) a CNU EPoC PHY has been linked, a CMC (or CLT) EPoC PHY can continue to transmit link configuration unicast messages to the linked CNU EPoC PHY (and in response receive a reply message from the linked CNU EPoC PHY) to determine if any further or additional adjustments need to be made to the configuration settings of the linked CNU EPoC PHY. For example, after having been linked (or even before), adjustments can be made to the transmit power and/or transmit delay of the CNU EPoC PHY. Other adjustments can be made to coefficients of a pre-equalizer at the CNU EPoC PHY used to pre-equalize upstream transmissions before the transmissions are sent to the CMC (or CLT) EPoC PHY.

IV. EPoC Network Upstream Frame Configuration

Upstream transmissions from the CNU EPoC PHYs 404 to the CMC (or CLT) EPoC PHY 402, including the reply messages described above in regard to FIG. 5 and MAC-level data, are organized into upstream frames that cyclically repeat. The exact configuration of these frames is determined in part by the link information included in the link info broadcast message received by the CNU EPoC PHYs 404 from the CMC (or CLT) EPoC PHY 402 at step 506 as described above in regard to FIG. 5.

FIG. 6 illustrates an exemplary configuration of an upstream frame 600 used in an EPoC network. Upstream frame 600 includes two types of sub-frames: a probe frame that spans P OFDMA symbols in time followed by Nf data frames that each span M OFDM A symbols in time, where P, Nf and M are integers. The spectrum of upstream frame 600 spans Ns OFDMA subcarriers where, in one embodiment, Ns is equal to the number of subcarriers in a single upstream OFDMA symbol. In one embodiment, the value of Ns is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5. Further details on the specific structure of the Nf data frames and the probe frame are described further below in turn.

In one embodiment, the Nf data frames have a fixed length in terms of OFDMA symbols of 256 and each of the Nf data frames has either M=8 or M=16 OFDMA symbols. Assuming each of the Nf data frames has M=8 OFDMA symbols, the number of data frames in upstream frame 600 is given by Nf=256/8 or 32. If, on the other hand, each of the Nf data frames has M=16 OFDMA symbols, the number of data frames in upstream frame 600 is given by Nf=256/16 or 16. In one embodiment, either the number of data frames Nf (i.e., either 32 or 16) or the number of OFDMA symbols M in each data frame (i.e., either 8 or 16) is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5. In other embodiments, the Nf data frames can have a different fixed length in terms of OFDMA symbols other than 256 and/or the Nf data frames can have a different number M of OFDMA symbols other than 8 or 16.

As further shown in FIG. 6, each data frame is further broken down into a column of resource blocks, where each resource block spans the M OFDMA symbols in time but only a single OFDMA subcarrier in spectrum. In one embodiment, the number of OFDMA symbols M in each resource block is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5.

Resource blocks can carry MAC-level data or data associated with the upstream PHY link channel. The upstream PHY link channel can be used by the CNU EPoC PHYs 404 to transmit reply messages upstream to the CMC (or CLT) EPoC PHY 402. For example, the upstream PHY link channel can be used by the CNU EPoC PHYs 404 to transmit the reply messages at steps 510 and 512 in FIG. 5 described above. In one embodiment, the upstream PHY link channel occupies 8 adjacent resource blocks from each of the Nf data frames and does not extend into the probe frame. In another embodiment, the specific number and/or location of the resource blocks that the upstream PHY link channel occupies within the Nf data frames is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5.

All remaining resource blocks from the Nf data frames not assigned to or occupied by the upstream PHY link channel can be used by the CNU EPoC PHYs 404 to transmit MAC-level data upstream to the CMC (or CLT) EPoC PHY 402. In one embodiment, the CMC (or CLT) EPoC PHY 402 can assign each resource block within a data frame not assigned to or occupied by the upstream PHY link channel to any one of the CNU EPoC PHYs 404 to transmit MAC-level data upstream. In addition, the CMC (or CLT) EPoC PHY 402 can assign, on a per resource block basis, a constellation size for the symbols to be transmitted over the associated subcarrier of the resource block. The constellation size determines the number of bits (or bit-loading) carried by the symbols transmitted over a sub-carrier. For example, a QAM symbol with a 64 point constellation can carry 6-bits of information. In one embodiment, the constellation size assignments is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5.

Referring now to the probe frame, in one embodiment the probe frame has a fixed length in terms of OFDMA symbols of 6. The probe frame can include one or more of a PHY discovery window, a fine ranging window, and a probe region.

The PHY discovery window was mentioned above in regard to FIG. 5. In particular, the PHY discovery window is a portion of the probe frame during which unlinked ones of the CNU EPoC PHYs 404 can send a reply message upstream to the CMC (or CLT) EPoC PHY 402 to allow the CMC (or CLT) EPoC PHY 402 determine initial range timing and transmit power of the unlinked ones of the CNU EPoC PHYs 404 and an address of the unlinked ones of the CNU EPoC PHYs 404. The reply message can specifically include a preamble to allow the CMC (or CLT) EPoC PHY 402 to determine initial range timing and transmit power of the unlinked ones of the CNU EPoC PHYs 404. The CNU EPoC PHYs 404 can subsequently adjust the transmit power and transmit delay of the unlinked one of the CNU EPoC PHYs 404 based on the determined initial range timing and transmit power. In one embodiment, the specific region of the probe frame that the upstream PHY discovery window occupies is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5.

After the CMC (or CLT) EPoC PHY 402 performs initial ranging and determines the address of one of the CNU EPoC PHYs 404, the CMC (or CLT) EPoC PHY 402 can direct the one of the CNU EPoC PHYs 404 to transmit upstream during a fine ranging window to permit the CMC (or CLT) EPoC PHY 402 to determine fine adjustments of the transmit delay and/or transmit power of the one of the CNU EPoC PHYs 404. In one embodiment, the specific region of the probe frame that the fine ranging window occupies is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5. The CMC (or CLT) EPoC PHY 402 can assign a particular one of the CNU EPoC PHYs 404 to transmit upstream during a fine ranging window using a unicast message to the particular one of the CNU EPoC PHYs 404.

The probe region of a probe frame is used by the CNU EPoC PHYs 404 to transmit known pilot patterns upstream to the CMC (or CLT) EPoC PHY 402. The CMC (or CLT) EPoC PHY 402 can use a received pilot pattern to determine a response of the upstream channel between the one of the CNU EPoC PHYs 404 that transmitted the known pilot pattern and the CMC (or CLT) EPoC PHY 402. The channel estimate can then be used by the CMC (or CLT) EPoC PHY 402 to determine or adjust pre-equalization coefficients of a pre-equalizer at the one of the CNU EPoC PHYs 404 to better match the channel response characteristics. In one embodiment, the specific region of the probe frame that the probe region occupies is provided to the CNU EPoC PHYs 404 via the link information in the link info broadcast message as described above in regard to step 506 in FIG. 5. The CMC (or CLT) EPoC PHY 402 can assign a particular one of the CNU EPoC PHYs 404 to transmit upstream during at least a part of the probe region using a unicast message to the particular one of the CNU EPoC PHYs 404.

The known pilots in the probe symbols (i.e., the symbols of the probe frame) can also be used to range CNUs in time offset and transmission power, for the fine ranging of new CNUs and for periodic maintenance of existing CNUs.

V. EPoC Network Upstream Pilot Provisioning

As described above in regard to FIG. 6, data frames within an upstream frame are made up of a column of resource blocks. Each resource block within a data frame can span 8 or 16 OFDMA symbols in time and a single OFDMA subcarrier in spectrum.

Beyond the basic size and positioning of resource blocks within a data frame, resource blocks can also take on different, predetermined types that, in general, determine a number and configuration, of pilots included in a resource block. For example, and in one embodiment, resource blocks can be assigned to one of three different, types: type-0, type-1, and type-2.

A type-0 resource block includes zero pilot symbols. Thus, all of the symbols in a type-0 resource block can be used to carry data, such as MAC level data, for example.

A type-1 resource block includes two normal pilot symbols on the first and third symbols of the resource block. All other remaining symbols of a type-1 resource block can be used to carry data, such as MAC level data, for example. A normal pilot, in contrast to a low density pilot, is a known symbol with a low-order constellation (e.g., BPSK). A low density pilot is a symbol that carriers data but with a smaller number of bits than the other symbols of the resource block used to carry data. For example, and in one embodiment, a low density pilot has four fewer hits than the other symbols of the resource block used to carry data.

Finally, a type-2 resource block includes two normal pilots and two low density pilots. The two normal pilots are on the first and third symbols of the resource block. The two low density pilots are on the last and third to last symbols of the resource block. All other remaining symbols of a type-2 resource block can be used to carry data, such as MAC level data, for example.

FIG. 7 illustrates the three different types of resource blocks 702, 704, and 706 for a resource block that spans 8 OFDMA symbols in time in accordance with embodiments of the present disclosure. Each square in a resource blocks 702, 704, and 706 represents a sub-carrier at a specific symbol time. Normal pilots are denoted by “P”, and low density pilots are denoted by “LD”. All other empty squares in resource blocks 702, 704, and 706 can be used to carry data.

As can be seen from FIG. 7, the type-0 resource block 702 includes zero pilot symbols. Thus, all of the symbols in the type-0 resource block 702 can be used to carry data, such as MAC level data, for example. The type-1 resource block 704 includes two pilot symbols on the first and third symbols of the resource block. All other remaining symbols of the type-1 resource block 704 can be used to carry data, such as MAC level data, for example. The type-2 resource block 706 includes two pilots and two low density pilots. The two pilots are on the first and third symbols of the resource block 706. The two low density pilots are on the last and third to last symbols of the resource block 706. All other remaining symbols of the type-2 resource block 706 can be used to carry data, such as MAC level data, for example.

FIG. 8 illustrates the three different types of resource blocks 802, 804, and 806 for a resource block that spans 16 OFDMA symbols in time in accordance with embodiments of the present disclosure. Each square in a resource blocks 802, 804, and 806 represents a sub-carrier at a specific symbol time. Normal pilots are denoted by “P”, and low density pilots are denoted by “LD”. All other empty squares in resource blocks 802, 804, and 806 can be used to carry data.

As can be seen from FIG. 8, the type-0 resource block 802 includes zero pilot symbols. Thus, all of the symbols in the type-0 resource block 802 can be used to carry data, such as MAC level data, for example. The type-1 resource block 804 includes two pilot symbols on the first and third symbols of the resource block. All other remaining symbols of the type-1 resource block 804 can be used to carry data, such as MAC level data, for example. The type-2 resource block 806 includes two pilots and two low density pilots. The two pilots are on the first and third symbols of the resource block 806. The two low density pilots are on the last and third to last symbols of the resource block 806. All other remaining symbols of the type-2 resource block 806 can be used to carry data, such as MAC level data, for example.

The pilots transmitted upstream in resource blocks can be used by a CMC (or CLT) for acquiring the frequency of carriers transmitted upstream from a CNU and/or for estimating the upstream channel between the CMC (or CLT) and CNU. To be able to effectively perform frequency acquisition and/or channel estimation (or even some other function), resource block types can be positioned within upstream data frames in accordance with particular pilot rules. In one embodiment, the pilot rules include using type-2 resource blocks on the boundaries of upstream data frames, the edges of an area of excluded sub-carriers, and the first and last resource block in an upstream transmission burst.

FIG. 9 illustrates an example upstream data frame 900 that adheres to these pilot rules in accordance with embodiments of the present disclosure. In particular, at the two upstream frame boundaries 902 and 904 of upstream data frame 900, a type-2 resource block is used. In addition, at the edges 906 and 908 of an area of excluded sub-carriers 910, a type-2 resource block is used.

In the remaining resource blocks of upstream data frame 900, an example pilot pattern is used. In particular, type-1 and type-2 resource blocks are alternately used every 4^(th) resource block in upstream data frame 900 with type-0 resource blocks used in between. The pilot pattern specifically begins at the bottom of upstream data frame 900 with a type-2 resource block, and does not interfere with the adherence of any of the pilot rules detailed above.

The example pilot pattern shown in upstream frame 900 is shown for exemplary purposes only. Other pilot patterns can be used in an upstream frame, such as upstream frame 900, as would be appreciated by one of ordinary skill in the art. To further be able to effectively perform frequency acquisition and/or channel estimation (or some other function), the CMC (or CLT) can configure the particular pilot pattern used in an upstream data frame, such as upstream data frame 900. For example, the CMC (or CLT) can configure the particular pilot pattern such that a type-1 resource block is to be used every x resource blocks of the plurality of resource blocks in the upstream data frame and a type-2 resource block is to be used every y resource blocks of the plurality of resource blocks in the upstream data frame, where x and y are integers. In one embodiment, CNU interface 330 in FIG. 3 is used to construct upstream data frame 900.

FIG. 10 illustrates another example upstream data frame 1000 that adheres to the above described pilot rules in accordance with embodiments of the present disclosure. In particular, at the two upstream frame boundaries 1002 and 1004 of upstream data frame 1000 and the edges 1006 and 1008 of an area of excluded sub-carriers 1010, a type-2 resource block is used. In addition, a type-2 resource block is used on the first and last resource block in the upstream transmission burst 1012, which is delineated by a dark rectangle. Upstream transmission burst 1012 represents a portion of upstream data frame reserved by a CMC (or CLT) for upstream transmissions from a particular CNU.

In the remaining resource blocks of upstream data frame 1000, the same example pilot pattern in upstream frame 900 in FIG. 9 is used. Again, it should be noted that the example pilot pattern shown in upstream frame 1000 is shown for exemplary purposes only. Other pilot patterns can be used in an upstream frame, such as upstream frame 1000, as would be appreciated by one of ordinary skill in the art. In one embodiment, CNU interface 330 in FIG. 3 is used to construct upstream data frame 1000.

VI. Example Computer System Environment

It will be apparent to persons skilled in the relevant art(s) that various elements and features of the present disclosure, as described herein, can be implemented in hardware using analog and/or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software.

The following description of a general purpose computer system is provided for the sake of completeness. Embodiments of the present disclosure can be implemented in hardware, or as a combination of software and hardware. Consequently, embodiments of the disclosure may be implemented in the environment of a computer system or other processing system. An example of such a computer system 1100 is shown in FIG. 11. Elements depicted in FIGS. 1-4 may execute on one or more computer systems 100. Furthermore, each of the steps of the processes depicted in FIG. 5 can be implemented on one or more computer systems 1100.

Computer system 1100 includes one or more processors, such as processor 1104. Processor 1104 can be a special purpose or a general purpose digital signal processor. Processor 1104 is connected to a communication infrastructure 1102 (for example, a bus or network). Various software implementations are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the disclosure using other computer systems and/or computer architectures.

Computer system 1100 also includes a main memory 1106, preferably random access memory (RAM), and may also include a secondary memory 1108. Secondary memory 1108 may include, for example, a hard disk drive 1110 and/or a removable storage drive 1112, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, or the like. Removable storage drive 1112 reads from and/or writes to a removable storage unit 1116 in a well-known manner. Removable storage unit 1116 represents a floppy disk, magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 1112. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 1116 includes a computer usable storage medium having stored therein computer software and/or data.

In alternative implementations, secondary memory 1108 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 1100. Such means may include, for example, a removable storage unit 1118 and an interface 1114. Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, a thumb drive and USB port, and other removable storage units 1118 and interfaces 1114 which allow software and data to be transferred from removable storage unit 1118 to computer system 1100.

Computer system 1100 may also include a communications interface 1120. Communications interface 1120 allows software and data to be transferred between computer system 1100 and external devices. Examples of communications interface 1120 may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface 1120 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 1120. These signals are provided to communications interface 1120 via a communications path 1122. Communications path 1122 carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels.

As used herein, the terms “computer program medium” and “computer readable medium” are used to generally refer to tangible storage media such as removable storage units 1116 and 1118 or a hard disk installed in hard disk drive 1110. These computer program products are means for providing software to computer system 1100.

Computer programs (also called computer control logic) are stored in main memory 1106 and/or secondary memory 1108. Computer programs may also be received via communications interface 1120. Such computer programs, when executed, enable the computer system 1100 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 1104 to implement the processes of the present disclosure, such as any of the methods described herein. Accordingly, such computer programs represent controllers of the computer system 1100. Where the disclosure is implemented using software, the software may be stored in a computer program product and loaded into computer system 1100 using removable storage drive 1112, interface 1114, or communications interface 1120.

In another embodiment, features of the disclosure are implemented primarily in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine so as to perform the functions described herein will also be apparent to persons skilled in the relevant art(s).

VII. Conclusion

Embodiments have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein, for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

The foregoing description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 

What is claimed is:
 1. A coaxial network unit (CNU), comprising: a CNU interface configured to generate a data frame that includes a plurality of resource blocks, wherein the plurality of resource blocks comprises a type-0 resource block, a type-1 resource block, and a type-2 resource block, wherein the type-2 resource block has two normal pilot symbols on a first and a third symbol of the type-2 resource block and two low density pilot symbols on a last and a third to last symbol of the type-2 resource block; and a modulator configured to modulate the data frame for upstream transmission over an Ethernet Passive Optical Network over Coax (EPoC).
 2. The CNU of claim 1, wherein: the type-0 resource block has no pilot symbols, and the type-1 resource block has two normal pilot symbols on a first and a third symbol of the type-1 resource block.
 3. The CNU of claim 1, wherein the data frame further includes the type-2 resource block on a first and a last resource block of the upstream data frame.
 4. The CNU of claim 1, wherein the data frame further includes the type-2 resource block on a first and a last resource block of an upstream transmission burst in the data frame.
 5. The CNU of claim 1, wherein the data frame further includes the type-2 resource block on an edge of an area of excluded sub-carriers in the data frame.
 6. The CNU of claim 1, wherein at least some of the plurality of resource blocks are arranged in the data frame in accordance with a pilot pattern.
 7. The CNU of claim 1, wherein the pilot pattern specifies the type-1 resource block is to be used every x resource blocks of the plurality of resource blocks in the data frame and the type-2 resource block every y resource blocks of the plurality of resource blocks in the data frame, wherein x and y are integers.
 8. The CNU of claim 7, wherein the pilot pattern is configurable.
 9. The CNU of claim 8, wherein the pilot pattern is configurable by a coaxial line terminal (CLT) to which the data frame is transmitted upstream over the EPoC.
 10. A coaxial network unit (CNU), comprising: a CNU interface configured to generate a data frame, wherein the data frame includes, on a first and a last resource block of the data frame, a type-2 resource block that has two normal pilot symbols on a first and a third symbol of the type-2 resource block and two low density pilot symbols on a last and a third to last symbol of the type-2 resource block; and a modulator configured to modulate the data frame for upstream transmission over an Ethernet Passive Optical Network over Coax (EPoC).
 11. The CNU of claim 10, wherein the data frame further includes the type-2 resource block on a first and a last resource block of an upstream transmission burst in the data frame.
 12. The CNU of claim 10, wherein the data frame further includes the type-2 resource block on an edge of an area of excluded sub-carriers in the data frame.
 13. The CNU of claim 10, wherein the data frame further includes a plurality of resource blocks arranged in the data frame in accordance with a pilot pattern.
 14. The CNU of claim 10, wherein the pilot pattern specifies the type-1 resource block is to be used every x resource blocks of the plurality of resource blocks in the data frame and the type-2 resource block every y resource blocks of the plurality of resource blocks in the data frame, wherein x and y are integers and the type-1 resource block has two normal pilot symbols on a first and a third symbol of the type-1 resource block.
 15. The CNU of claim 14, wherein the pilot pattern is configurable.
 16. The CNU of claim 15, wherein the pilot pattern is configurable by a coaxial line terminal (CLT) to which the data frame is transmitted upstream over the EPoC.
 17. A coaxial network unit (CNU), comprising: a CNU interface configured to generate a data frame, wherein the data frame includes, on a first and a last resource block of an upstream transmission burst in the data frame, a type-2 resource block that has two normal pilot symbols on a first and a third symbol of the type-2 resource block and two low density pilot symbols on a last and a third to last symbol of the type-2 resource block; and a modulator configured to modulate the data frame for upstream transmission over an Ethernet Passive Optical Network over Coax (EPoC).
 18. The CNU of claim 17, wherein the data frame further includes a plurality of resource blocks arranged in the data frame in accordance with a pilot pattern.
 19. The CNU of claim 18, wherein the pilot pattern specifies a type-1 resource block is to be used every x resource blocks of the plurality of resource blocks in the data frame and the type-2 resource block every y resource blocks of the plurality of resource blocks in the data frame, wherein x and y are integers and the type-1 resource block has two normal pilot symbols on a first and a third symbol of the type-1 resource block.
 20. The CNU of claim 19, wherein the pilot pattern is configurable by a coaxial line terminal (CLT) to which the data frame is transmitted upstream over the EPoC. 